Solve the following measurement conversion problems: State the relationships between kilometers, meters, centimeters, and millimeters. Convert the following to kilometers: a) 4200 m, b) 800,000 cm, c)

The relationships between units of length measurement are:

• $1 \text{ kilometer (km)} = 1000 \text{ meters (m)}$
• $1 \text{ meter (m)} = 100 \text{ centimeters (cm)}$
• $1 \text{ centimeter (cm)} = 10 \text{ millimeters (mm)}$

2. Convert to kilometers: a) Convert $4200 \text{ m}$ to $\text{km}$:

   $$4200 \text{ m} \times \frac{1 \text{ km}}{1000 \text{ m}} = 4.2 \text{ km}$$

   b) Convert $800,000 \text{ cm}$ to $\text{km}$:

   $$800,000 \text{ cm} \times \frac{1 \text{ m}}{100 \text{ cm}} \times \frac{1 \text{ km}}{1000 \text{ m}} = 8 \text{ km}$$

   c) Convert $645,000 \text{ m}$ to $\text{km}$:

   $$645,000 \text{ m} \times \frac{1 \text{ km}}{1000 \text{ m}} = 645 \text{ km}$$

   The answers are: a) $\boxed{4.2 \text{ km}}$, b) $\boxed{8 \text{ km}}$, c) $\boxed{645 \text{ km}}$.

3. Convert to the required units: a) Convert $6 \text{ m}$ to $\text{mm}$:

   $$6 \text{ m} \times \frac{100 \text{ cm}}{1 \text{ m}} \times \frac{10 \text{ mm}}{1 \text{ cm}} = 6000 \text{ mm}$$

   b) Convert $22000 \text{ mm}$ to $\text{m}$:

   $$22000 \text{ mm} \times \frac{1 \text{ cm}}{10 \text{ mm}} \times \frac{1 \text{ m}}{100 \text{ cm}} = 22 \text{ m}$$

   c) Convert $9 \text{ km